Hi,
aggr add can work.
I was confused on the situation you met. I have 2 spare disks in the pool. But my aggr need more data space.
I run aggr add and got warning. I quit!!!
aggr add aggr1 -d 0a.26 0a.42
WARNING! Continuing with aggr add will result in a
low spares disk condition for one or more RAID groups.
Are you sure you want to continue with aggr add? n
I think it need spare disks in the pool. So how many spare disks it need? I have 2 Disk shelf, so I think maybe 2 spares.
At last, I tried add one disk, it succeed.
aggr add aggr1 -d 0a.26
Addition of 1 disk to the aggregate has completed.
So I think it is better left one spare for pool.